External USB disks in BackupExec 2012

Hi,

I use a BE 2012 in a windoes server 2008 R2 and started make backups to external usb disk, configured a storage pool with 3 disks and works well, I found that needed more, I tried  create disk storage before adding to the pool already configured but, the new disk though seen by the OS is not recognized by BE, and I can not add it, disconnect all disks and connect just the new (never used in the poll) is automatically recognized as the first disk pool. How I can resolve this situation?

Anyone can help? Thanks.
VM